Impressions of the Celestron CG-11 Telescope

Company Seven actually sells more C-11 and C-14 telescopes than we do C-8's since people who really want their system made well, and properly set up so value Company Seven's support. This can be an observatory class instrument, and there are numerous options which you are likely to choose to buy initially with the telescope, and then many more can be added over time to further increase the versatility of this telescope. Please contact Company Seven for a more in depth reply either by Email, or by telephone, or at our showroom,

On 16 June 1992 Company Seven received the first of our new Celestron C-11 telescopes on the Losmandy Model G-11 German equatorial mount. As is the policy of Company Seven to inspect every telescope we sell, we decided to note our first impressions of this standard production telescope. Celestron and Scott Losmandy were provided a copy of this review to help refine the product. If there are suggestions of improvements to be made here, or mention of any problem we noted, these will have been considered by Scott and Celestron before the public reads this.

This review assumes persons considering such a telescope are familiar with telescope general attributes and with certain basic terms such as declination (DEC), right ascension (RA), polar alignment, tracking rates, etc. Therefore, these will not be explained herein. One of our expectations is that a buyer with prior experience may in their excitement overlook the instruction manual, and proceed with assembly. If that user had prior experience with the Losmandy GM-100 mount, then this effort is facilitated since the G-11 is an evolution of the Losmandy GM-100 mount marketed through Scott Losmandy's "Hollywood General Machining". When Company Seven first learned of the CG-11 telescope we were optimistic for a number of reasons:

1. Scott Losmandy has good mechanical design experience and the in-house computer controlled manufacturing equipment necessary to produce precision machined components consistently.

2. The Celestron C-11 has been our favorite Schmidt-Cassegrain optical tube. For a little more work than hauling an 8" telescope, the C-11 gives 1.9X the light gathering power of a 8" Schmidt-Cassegrain. This improvements in light gathering power translate into better views and photos with the C-11 of the faint deep-sky objects without going to the back breaking C-14. The contrast and overall image quality will often outperform competing larger telescopes which may be inferior in design or quality of manufacture.

3. What we did seek in improvements over the previous Schmidt telescopes pertained to optical consistency, mirror shift during focusing, mount stability, and transportability. These have been improved by the current administration at Celestron; even though we find an occasional anomaly, our tests of each production C-11 telescope we that receive show improvement.

   It is obvious that Celestron has upgraded the fork mount systems over the years to varying degrees. But the fork mounted 10" and larger Schmidt-Cassegrain models remain quite a handful for most casual users. This move of Celestron into premium German equatorial mounts provides the user with two very important features:

   1. The CG-11 telescope is not lightweight as a whole but it is easy to disassemble and transport. The heaviest single component is the G-11 equatorial mount head which weighs in at 31 lb. The optical tube, with 8x50 finder scope, lens shade, and standard visual accessories does also weigh in at 31 lb. This compares favorably against the fork mounted Celestron Ultima C-11 at 53 lb., and the Meade 2120 LX200 at 61 lb.
   2. The G-11 is a tracking platform that can accept a wide variety of photo visual telescope systems due to its precisely fitted, quality components. Therefore a customer who has a C-8 or a 4" refractor (up to f15) now may upgrade the mount, and later the optics. One can be out with a C-11 hunting faint planetary nebulae on one night, then switch to a Astro-Physics apochromatic refractor for planetary observing, or ultra-wide field views or astrophotography.

4. Previously if Scott Losmandy had any, the "Achilles Heel" had been his erratic delivery schedule, and "buggy" tracking and control electronics of the past. Some of the first GM-100 mounts had electronics (made by a sub-contractor) which were recalled and replaced by Scott. This time Scott incorporates the latest advances in proven electronics technology to assure very precise tracking accuracy without the need to go to larger (and more expensive) worm gear drive sets, even though the gear and motor sets on this mount are already impressive.

UNPACKING AND ASSEMBLY:

The CG-11 telescope arrived at Company Seven via U.P.S. by ground. With 6 separate cartons less than 70 lb. per package this allows economical shipping in the U.S. by services such as United Parcel Service. The total weight of these boxes is 182 lb., which translates into a U.S. coast to coast shipping fee of $86.53 - this does not include fees for insurance. At Company Seven, we prefer to ship some Schmidt-Cassegrain optical tubes by air to reduce the risk of damage in transit.

The C-11 optical tube arrives in a 16-1/2" x 16 x 30-1/2" foam lined traditional Celestron telescope carrying case, within doubled cardboard outer boxes. The inner carrying case bottom was damaged probably when dropped with enough force to cause the foam at the bottom of the case to compress. This allowed the dovetail mounting plate attached to the telescope tube to clearly indent and crack through the carrying case. As part of our inspection and quality assurance program, we noted this and asked Celestron replace the damaged case.

We conceded that we should read the instruction manual before continuing - this is not to say we actually did read the manual. The setup is fairly straight forward. A leg clamps is installed onto each tripod leg; this is a first-time set-up procedure only. Each of three legs slides onto the "semi pier" central column. This required more than a modicum of effort; in fact the fit was so tight that we had to abrade the fittings to fit. The standard legs with the central column provide a platform 48" tall for the G-11 head. There are optional legs available for this mount of 260 and 600. This height is perfectly adequate for stand-up observing, but a bit too high if the observer is seated even on a high chair. An aluminum pier for permanent installation is also available. The G-11 head is furnished with a 16-1/2" x 17" x 9-3/4" Airline Transport Approved aluminum reinforced, fiberglass clad, dense foam lined case. The G-11 head set for latitude 38 degrees just fit into this case. The head slides onto a 5.525" inner diameter tripod central column, then is secured by three 7/32" bolts. Here our second mishap was discovered, the mount arrived with a 1/4" Hex wrench instead of the 7/32" wrench. That overcome, the G-11 head was secured. The bolts attaching the G-11 head to the central column should be "wrench tight" to maintain overall rigidity.

The machined stainless steel counterweight shaft threads into the DEC Axis. This required some effort, but was facilitated by applying a light oil to the counterweight shaft threads - care was taken to work the shaft in and out gradually until it was easy to do. The shaft and the socket for the shaft were cleaned to remove any oily residue. The counterweight shaft of this mount had eight small gouges running in a helical pattern near the male threads, this did not affect performance and was production related. The two counterweights weigh 11 lb. each. These slide onto the 13" long shaft and are each secured by a hand knob; a shaft safety stop is also provided. The machined steel, painted counter-weights required some fine bore sanding to get the weights onto the shaft. It seems the paint thickness was greater than anticipated. The finish on one counterweights had areas that were elevated, it was bubbled paint due to minor surface rust.

The C-11 tube has a precision machined dovetail (male) plate attached, this slides into the G-11 head saddle. The C-11 slid into place quite precisely in our showroom. The dovetail was secured by turning one aluminum knurled knob. The standard ocular is a Celestron Ultima 30mm 1-1/4" Plossl; it is a good quality accessory which will run at 93X and show 0.54 degrees field of view on a typical C-11 telescope - in other words a good first view of the moon! The 8x50 finder scope has a new quick release bracket by Losmandy. This bracket is secure and precisely machined; it does not have the vulnerability to impact that the lightweight Celestron 8x50 fixed bracket has, and with set screws on the front and rear rings the finder is now much easier to adjust and secure. A quick release bracket allows the C-11 tube to fit into a smaller crate for transport; the bracket may also accept other accessories. The 8x50 convertible (allows right angle or straight through viewing) Polar Alignment Finder with illuminator was then installed. The CG-11 is so tall that most users will set the finder for straight through viewing. Since the G-11 mount includes an illuminated Polar Alignment finder (up to a $150 option on most other mounts), a less expensive conventional 8x50 finder could have been supplied instead but we have no objection to the existing finder which allows a field of view of 5.4 degrees, but Celestron will continue to furnish the finder we see on this telescope.

The integral G-11 mount illuminated Polar Alignment finder telescope is a first for the Losmandy line. This finder incorporates an etched reticle to aid polar aligning the equatorial mount; this is easier to use than conventional polar finders that are mounted onto the telescope optical tube. To illuminate the reticle a light emitting diode (LED) is threaded into place near the finder eyepiece; this must be attached after the finder is in place, and removed before the finder is removed to avoid having the finder retaining ring bind against the illuminator. The illuminator is powered by two AA batteries (3 volts in series) in a pouch; this eliminates the need to locate button sized batteries used on most other Polar finder illuminators. It would be more convenient and possibly cost effective to power the illuminator from the mount control console. An added bonus is the finder reticle has north and south hemisphere alignment patterns, if the LED was brighter we might actually be able to see all the reference star positions in the finder reticle! To install the finder scope, a precisely machined aluminum cover unscrews to reveal the threaded opening for the Polar finder. This finder threads into the R.A. axis. Now the telescope is pointed west until the DEC shaft perforation lines up with the finder scope to allow viewing north. Another precisely machined aluminum cover threads into an opening on the DEC Axis to keep dust and dirt out when the Polar finder is not in place. The precision and mechanical quality of even these minor cover fittings speaks volumes - this is a mount with few compromises. Even if the mount is elevated to the highest latitude setting, the illuminator and finder scope do not bind against the G11 mount.

The mount has a laser engraved latitude scale. This scale is easy to read, and covers the range from 10 to 66 degrees in 2 degree increments. If the user can not see any reference stars to align the mount, he can align using a compass, levels, and latitude scale. If the user is even within 5 degrees of true north then this will be adequate for observing. Other techniques (star drift, etc.) may be used to refine alignment further.

The only optional accessory we installed was the new Celestron C-11 lens shade. In the mid-Atlantic region dew and glare from nearby lights are such a problem that most of our customers use a shade. The slip-on shade has a black finish exactly matching the front and rear cell paint scheme on the C-11. For the most humid nights an optional heater or a heated hood (such as our Tuthill "No Du Cap" models) are recommended. To conclude setup, we attached the DEC and R.A. motor power cables, and the hand control box to the Model #492 Electronic Control Console.

After all accessories were attached, the telescope was balanced for viewing in R.A. and DEC. The two counterweights are adequate for the load of the telescope with standard accessories, but there is not much reserve for larger accessories. With a relatively lightweight optional lens shade in place, the counterweight shaft safety stop thumbscrew was let out a bit to allow the counter-weights to be placed far enough out to nearly balance the telescope. We suggest that users buying the CG-11 could be furnished with a shaft that is longer or an extension, and the existing shorter shafts be supplied with persons buying the mount alone. The user should purchase an additional counterweight if the telescope is to use 2" accessories, or a camera.

Now the telescope was starting to look like a serious research grade instrument - if only Celestron had furnished matching plug/screws for the fork mounting holes at the C-11's rear cell instead of just leaving them taped over!

THE DRIVE SYSTEM

The revolution in electronics has increased the potential tracking accuracy in mountings and has facilitated making positioning adjustments. Gear diameter is no longer the only measure of tracking accuracy in a mount. Increases in the speeds at which a telescope may be "panned" across an area have nearly relegated manual slow motion controls to museum pieces and the least sophisticated telescopes.

The R.A. and DEC drive system employs identical 5.625" diameter 360 tooth main gears manufactured from 7075 T35 aluminum stock. The worm is of bulletproof 440C with a high 54 Rockwell hardness rating. There are adjustable clutches in DEC and R.A. permitting the user to engage the electronic drives, to vary how "stiff" the telescope is to manual movement, or to compensate for slight imbalances caused by interchanging accessories. The workhorse of the drive electronics are the reliable high torque (140 oz-in @200 p/s) Hurst ABS series geared permanent magnet stepping motors. These motors have an input power rating of 4-1/2 watts and are rated for long life at rated loads. If one considers how few the hours are over the years that a telescope is actually tracking, we expect a lifetime of trouble free service from these motors. The Hurst catalog indicates the motors have 150 reduction, by accessing 1/2 steps a tiny 0.05 degree (0.50 arc second) step angle results. This translates into 7,200 steps per complete revolution. Each motor is direct coupled (Oldham coupling) to the worm gears. The motor wiring harness interfaces to a 6 conductor modular jack on a weather resistant circuit board. The motor, harness and jack are covered by a snug, fitted molded elastic cover. The coiled electrical cables which connect the DEC and R.A. motors to the control console are about 24 inches long (compressed) but easily expand to accommodate the mount through its motions.

The 5" x 5" x 1" electronic control console houses the digital drive control system. It is secured with two 1/4"- 20 knobs (each is a machined out of one block!) on flanges which protrude from the tripod central column. It is well positioned as furnished from the factory for convenience and protection of the console. Being removable, facilitates later upgrades. The console back and sides are actually one solid hogged-out, and satin black anodized block of aluminum with walls averaging 9.25mm (.36") thick! The cover plate is an adequate 1.5mm thick. The electronic components are not crowded, of good quality, and the assembly and soldering is nearly NASA space flight quality! The control console display is simple to comprehend, and intelligently laid out. The electronics permit the mount to do what mounts should do best - track precisely, and permit controllability. The switches are nearly flush to the panel, but protrude enough to be actuated by a gloved hand. The console controls are push buttons separated just enough to accommodate a gloved hand. These controls are:

1. G/S - Guide Setting with three photoguide rates ( 30%, 50%, and 2X sidereal rate) and three setting rates (4X, 8X, 16X sidereal rate). At start-up the default rate is 0.3X. Although the telescope may be set at the panel to a slow guide rate, it is possible to override, then move the telescope in R.A. and/or DEC at the 16X rate from the hand control box.

2. TVC - Time Variable (Backlash) Correction function. The TVC need be set only for astrophotography, and only once when the telescope is powered up. During precise tracking the DEC is not constantly running as the R.A. motor does. This circuit eliminates backlash in the DEC motor gears which may be reversed periodically by the user when doing drive corrections. This is typically in response to an "over correction as during a photo session the corrections in DEC typically occur only in one direction. When activated and properly adjusted and while operating at the slower guiding rates commonly used in imaging, if a user changes the direction of the motion in DEC then the TVC circuit will speed up the stepper motor briefly (and almost imperceptibly) to take up any backlash.

   There are 10 possible settings controlled by the TVC button; these settings are shown by an illuminated green bar display to the right of the switch. The display brightness is adjustable. At the slowest setting, the stepper motor runs at four times (4X) the sidereal rate for 0.003 seconds; each step faster increases the length of time the motor runs by another 0.003 seconds. The user sets the TVC by looking through the telescope at a target, and adjusting the setting until the backlash has been eliminated. According to the factory, a setting of between three to six bars is typically adequate. At the faster settings the backlash was barely perceptible, and was certainly less than 8-10 secs without the TVC engaged; with the TVC it was not perceptible at 200X (our sky limit that night).

3. RATE - Selects one of four quartz tracking rates (sidereal, solar, lunar, King). The default rate is sidereal rate which drives at one rotation in 1,436.5 minutes (according to Celestron - we did not run a stopwatch to check this).

4. PEC - Periodic Error Correction circuit reduces the number of periodic tracking corrections that a user does to reduce the amplitude of worm gear errors. The PEC circuit is programmed by the user guiding one revolution of the worm (for 4 minutes); the PEC circuit then automatically takes over. With PEC engaged worm tracking error is reduced to virtually imperceptible levels. We did notice something is favorably peculiar about this PEC circuit - it does seem more accurate on long exposures than the first generation PEC systems we tested. This variance may have something to do with the overall mount stability, but we think there is more to it than that and we will follow this up if the weather clears again in Washington, D.C.

5. DIM - to adjust the brightness of the red LED displays at the console and hand control box, and of the green TVC display on the console.

Other jacks on the control console accommodate 12 volt DC power in, and 12 volt DC outlet for options such as a guiding reticle, digital display setting circles, or a heated hood (our C-11 heated hoods draw about 1 amp). The outlet has a maximum suggested 2.5 amp load (according to Scott), any more than this can blow the board since there is no internal fuse protection.

The hand control box jack is labeled "HC/CCD" since the system is designed to accommodate autoguide optional charge coupled device (CCD) systems - by definition this is our Santa Barbara Instruments Group Model ST-4 ($990), although these other SBIG imaging systems also perform the autoguide functions: the Model ST-6A ($2650) system, or Model ST-7 ($2650) and Model ST-8 ($6450) systems. The hand control has N-S, E-W buttons, with switch reversing switches. Users might attach a small strip of Velcro to the hand control box and mount. As provided from the factory we found ourselves giving more attention than we should to finding a place to hang the box by its cable. Remember - attach the Velcro hook section to the mount to avoid having the hand control "grab" your clothing.

The telescope R.A. drive can be instructed to track in the Southern hemisphere mode in two ways: 1. remove the electronic console cover plate to access the "N-S" switch, or 2. powering "on" the telescope with the appropriate R.A. button pressed. We find either to be convenient and simple to use, but if one is going South its probably best to set the "N-S" switch.

Power requirements listed are 12 volts DC negative ground at 500 milliamps; a 13 watt rated 120/220 volt AC power adapter is furnished with the mount. This AC adapter put out 13.9 volts DC under load to the mount. The mount will run at as low as 10 volts or so however, the user begins to lose functions gradually as the voltage drops; for example at 10 volts, the 16X function lacks the voltage to function. Based on the average use our 12 volt 12 Amp Hr. pack should run the mount for about 24 to 36 hours!

MECHANICAL & ELECTRONIC OBSERVATIONS

Most of this mount is precision machined from virgin aluminum and stainless steel stock. We keep coming back to that word "precision" which in the context of Losmandy machining is not an overstatement. Many of the G-11 head components are of 6061 T-6, this is among what is specified by federal government agencies for bulletproofing material! The mount head, dovetail male and female plates, and counterweight shaft are machined. The shaft is natural stainless steel, most other parts are satin black anodized. This allows precise fitting of components, and assures a more professional appearing, and durable finish than many painted heads. The tripod and center column are painted but can easily be sanded and repainted if they're scratched.

We have learned that at times too much precision may be less than optimal. For example, the C-11 tube slid onto the mount easily at the first set-up in our showroom. But in the dark, during the first field trials we had a difficult time lining up the dovetail plate to the mount saddle, or dismounting the telescope. Since for safety most users install the tube when the mount has the counterweights on, with the shaft pointing to the ground, the user must hold the C-11 at least 65 inches off the ground to line up the mounting plate. Also, there is a tendency of the saddle to bind or resist fine adjustment (such as during balancing); if the dovetail plate were more smoothly surfaced and gloss anodized it might make sliding the back and forth a bit smoother. The C-11 tube is not exactly a flyweight chunk to get hung up with in the middle of the night.

On the first day the CG-11 was in our showroom, a customer (thinking the large aluminum knob on the side of the saddle was a DEC clutch control) loosened it causing the optical tube to slide violently down the saddle. Two mounting screws at the north end of the dovetail prevented the tube from slipping off of the mount, and the tube was grabbed by another customer before it slid that far - but all in the area were in shock for a moment. We suggest users be particularly aware that knob is not a clutch control. Possibly a second safety may be furnished (as on the GM-100), or color code or change the knob feel to make it less attractive to the uninformed.

Balancing the CG-11 in R.A. is simple, but in DEC caution should be the watchword. Never allow the C-11 tube to come out of your grip when balancing the scope; with the mount saddle loosened enough to allow sliding the C-11 tube back and forth, it is possible that if the tube dips forward (North) it may slid off the mount! One may pull south on the tube at the carrying handle on the rear cell. Pulling north is best managed by grabbing any exposed length of dovetail plate. The tube can not slide off to the south because two bolts that fasten the dovetail to the front of the C-11 tube protrude into the path of the saddle. A removable safety pin might be a good suggestion to mitigate the risk of having the optical tube slide off the plate to the north. If the buyer frequently uses similar accessories requiring balance at about the same place, they may tape or inscribe an "indexing" mark at the side on the exposed lip of the dovetail plate.

The mount has laser engraved R.A. and DEC circles. These are each 5" in diameter and can be read to a resolution of 1/4 degree in DEC, and 1 minute in R.A.. The R.A. circle is on a slip clutch which allows the circle to turn with the R.A. drive system motion. The telescope DEC circle was not set at the factory. This initial adjustment is performed here at Company Seven as part of our normal check-out service; a description of this procedure is in the "Celestron CG-11 Instruction Manual". The R.A. and Dec. axes are factory drilled and tapped to accept mounting hardware for encoders. The encoders planned by Losmandy will be manufactured from what else - aluminum! No plastic here either. There will be metal mounting brackets of at least 1/8" angle as well! These encoders should feed a range of accessories: digital display setting circles, computer databases with computer interfaces for software programs that we offer. This facility leaves the door wide open to a closed-loop computer control system if the main gears can handle it.

Polar alignment is nearly fool proof due to the accuracy of the aids and mount fine positioning controls. A laser engraved latitude scale is provided on the east side of the mount, it is right on the mark for accuracy and is superior to the typical "stick-on" variety. Two bubble levels are manufactured into the base of the G-11 head. These levels are recessed for protection, are easy to read, and are another example of the fine attention to detail on this mount. While a mount does not need to be level to be polar aligned, and the legs do not adjust length to level the head they may assist some who can set up in level areas at similar latitudes. The manual elevation and azimuth controls are jewel smooth, and very easy to manipulate even under the full load of a C-11 telescope. The precision machined aluminum knobs facilitate this. These controls allow a range of adjustment in elevation from 12.5 to 65 degrees (an optional accessory increases this to from 0 to 84 degrees according to the factory). At about 12.5 degrees the manual elevation knob contacts the R.A. worm housing, at 16 degrees the counterweights on the shaft can bind with the northern tripod leg. The elevation control does not reach 90 degrees therefore, this mount can not be used in an "Alt-Az" (up-down, left-right) mode; in our experience few German mounts have that ability and in practice it is rarely done anyway. Still, since this mount is bound to be purchased for use with 4" to 5" refractors, that ability would allow the mount to be used for panoramic, terrestrial viewing. We think a long handled Hex wrench should be provided to insure the customer has the leverage necessary to rigidly lock the R.A. axis latitude adjustment in place. The manual adjustment in azimuth (left to right) allows +- 8.5 degrees of movement.

The R.A. and DEC axes each incorporate 5 preloaded ball bearings each. When the mount is properly set, there is no perceptible play related to these bearings. Our G-11 head had notable play in R.A.. One could grasp the counterweight shaft and (with the R.A. clutch very tight) see obvious movement of between 1/4 to 1/2 degree as the shaft was moved back and forth. This was not backlash since when the telescope was properly balanced and the electronics were responding, the responses were smooth and quick. While tracking in R.A. we did timing tests to determine motor direction change response times. We were surprised that it took an average of 2.4 seconds for any perceptible reversing (viewing at 93 and 186X) with the guide setting at 16X. This problem was related to a loose worm gear; upon examination, we found the worm gear was loose in the block. After a few minutes of breakdown and reassembly, the problem was resolved.

The G-11 does not have manual slow motion controls. Our team had two different reactions to this: #1. As long as 12 volts DC are available such controls are really a luxury that is not essential. Also when one considers the variety of length of the telescopes that could be used on this mount such controls might be hard to fit or reach. With the clutches properly adjusted, the user can simply and quickly point the telescope towards the target, then use the electronic motors (at up to 16X) to center the target precisely in the field of view. Without power, it will be a long night. or opinion #2. The telescope 16X is not fast enough to offset the lack of slow motion controls, and some observers don't want to have to rely on power being available.

The tripod feet are metal so care should be taken when moving the telescope onto floors which may be scratched or dented. If a rigid collapsible tripod were available it would make the G-11 easier to pack for travel, and simpler to adapter for a person using several different telescopes on the head. The existing arrangement does not allow for height adjustment to suit various users although for a C-11 it is comfortable for most standing persons.

MISCELLANEOUS

The "Celestron CG-11 Instruction Manual" is well written and illustrated with numerous drawings. We found some errors in specifications but operational procedures were good. This manual should be kept with the telescope as a good reference. At the front is the customer registration card which really should be completed and returned to Celestron. Celestron could be advising customers of future developments by direct mail.

The CG-11 telescope does not have any obvious engraved Serial number on the optical tube (as is usual with Celestron), or on the mount. While Celestron is not alone in this practice, we think this is not a good idea for several reasons: 1. it is virtually impossible to identify and recover stolen property without a S/N, 2. it is difficult for Company Seven to track those telescopes we have "Passed"; only our C-VII labels identifies the telescope and mount was sold through us but not to whom or when, 3. it is difficult for the manufacturers to issue selective recalls (if ever necessary), 4. it is difficult to track overseas and U.S. sales of these products, 5. warranty issues may be clouded .

There is a wide selection of accessories by Celestron and after-market uppliers to better set up the CG-11 for a wide variety of uses. Several of these have been mentioned, particularly those that apply to the mount. Some accessories are in the Celestron CG-11 hand-out literature. But curiously enough, a copy of that flyer and a copy of the informative "Celestron Accessory Catalog" was not included with our first CG-11 telescope. This is not to say that everything in that catalog is the best option for everybody, but since we offer so many of the best available product lines we are in an excellent position to support our customers particular needs.

THE C-11 OPTICAL TUBE:

Since the C-11 tube suffered a bit in shipping, and we wanted to get this first impressions review to Scott Losmandy and Celestron, we did not go into the particulars of the C-11 optics. We discuss C-11 performance only in generalities and base any data on what is average in our individual telescope tests. While we may occasionally find a problem that we can not adjust out, our experience shows optical consistency of production Celestron Schmidt-Cassegrain telescopes has improved notably since the mid 1980's. Shipping damage and missing or wrong parts has been less of a problem, but even out of alignment the mirror shift on our CG-11 is still obvious. This is something we know Celestron has been working to reduce.

The Celestron C-11 has been our favorite Schmidt for some time. Whatever weakness may be perceived of the Schmidt-Cassegrain, for most observers these are outweighed by the tremendous easily transportable light gathering power, and overall quality of view the C-11 offers. After one considers the maximum central obstruction of 3.975" (secondary mirror baffle), and light loss in the system, a C-11 still passes more light than a 10" f6 Newtonian or a 9" apochromat of first quality. This is not to say we suggest the C-11 over a $25,000 Apo, but it shows that for faint deep sky objects this is a good value. And while a good 10" f6 at about $3000 can give superb views and photos of brighter objects, few people can transport that load, and most production mounts sold with Newtonians are comparatively primitive. For views of brighter objects such as the sun, moon, planets, and even some brighter deep sky objects it will take a >$5,900 investment for an Apochromat on a similar quality mount with similar accessories to surpass the C-11 for detail resolution. So when one considers the alternatives to a Schmidt, these generally involve notably more weight, bulk, and or cost.

A C-11 out of the box can not record the full moon or Sun on a 35mm film, its' nominal 2800mm focal length (which is good for planets, galaxies, and faint planetary nebulae) produces an image less than 1/2 degree on the vertical of the 35mm film. Celestron offers a matched positive lens that threads into the 2" back of the C-11. This accessory allows the C-11 to record 1.1 x 3/4 degrees, it works well in spite of some vignetting (due to a 41mm aperture), and gets the telescope down to a nominal effective focal length of 1765mm at f6.3. This light gathering and field of view makes the scope well suited to portable CCD imaging. Our Santa Barbara Instruments Group ST-6 will capture a field of view of about 1/4 degree by 1/3 degree. There are optional positive lenses that can increase this even further. Using a positive lens in the rear of a telescope as opposed to going with a faster mirror design assures the image brightness does not become perceptibly affected, that is aside from the few percent loss at the positive lens. Having the secondary mounted on a lens, as opposed to on a spider vane such those on Newtonian eliminates diffraction spikes from astrophotos.

For high magnification observing 1-1/4" accessories are adequate. We suggest the wide-field deep sky observer consider 2" accessories since a C-11 with the widest field of view 1-1/4" ocular shows only 0.6 degrees of sky with a 4.0 mm exit pupil. Using a quality 55 Plossl produces a 1.0 degree field of view with a 5.5mm exit pupil. Several of our customers even employ our larger diameter positive lens to get the telescope to show 1.4 degrees at 6.0mm exit pupil, a 55 Plossl shows 1.5 degrees with a 8.3mm exit pupil, but for people with a 7mm goal a 45mm would suffice at 6.8mm.

If you intend to get into astrophotography with the CG-11 we suggest a sheltered location, a good 35mm SLR body with a counterbalanced shutter (or the hat trick on long exposures), and a clear focusing screen such as the manufacturer suggests for astrophotography or macro photography. Also, buy an extra counterweight, and be prepared for an investment in accessories from a low of about $150 for simple wide sky "piggyback" photography, or $50 to $100 to shoot the planets or moon. For good deep-sky astrophotography budget $300 to $500 for an off-axis guider or guide telescope. If you intend to use a CCD autoguider, we suggest our SBIG ST-4 which with interface cable which will add $890 to that.

CONCLUSION:

There is nothing that is vital to good telescope operation, successful astrophotography, or CCD imaging that is not already included or available as an option for this platform. The machining is first rate and consistent, the quality and thickness of materials used throughout makes some other competitive products (particularly many not so cheap overseas mounts made of castings and thin or soft aluminum components) pale by comparison.

As of June 1992, this mount is the best mount on the market that we have seen anywhere near its' price. The stability is very good for such a compact head but a C-11 is the load limit for the average user, a bit beyond for the most discriminating. A short telescope of up to 40 or so pounds may be mounted for visual applications if there is none or a light wind, and we expect to see customers buy this mount for use with some long and high torque scopes up to a 23 lb. Astro-Physics 6"f9 EDT Apo for visual use - although it may be shaky in a breeze and such a long telescope can bind against the tripod central column when viewing overhead. For astrophotography (due to the added mass and torque from associated off axis guiders or guide telescopes) from an average environment we would limit this to a C-11 tube, or a long 5" Apo tube. With no wind such as from within a dome for example, it is not unlikely that good photos will be had with larger telescopes.

Several of the comments related above (mounting, dismounting, finder height) would have probably not been as problematic if the mount was a few inches shorter, we also expect several of the issues will be remedied soon. At C-7 we can not afford to be as price competitive if we have too many things to adjust out of a product during check out. This version of the C-11 will be popular with people who do not have a vehicle which fits the C-11 Ultima (in its case), or those who have a preference for German mounts, or for those who have several telescopes that could be used on the G-11 head. For those who want a quicker setup, and can tolerate the bulk and approximate 70 lb. load of an Ultima 11 on its fork/drive, or for those who find the fork mount more user friendly then the Ultima 11 remains a viable option. We urge the Ultima 11 buyer consider upgrading the standard wedge to the new heavy duty wedge as well as the tripod.

This system packaged with the C-11 optical tube is selling in the low $3000 range and we rate it a best buy in the portable deep-sky class. It would take a lot more money to equal it for certain astronomical uses. The G-11 equatorial mount is almost too good to be true for the upper teens complete! This mount and others made of similar quality will be around a number of years still looking good, and doing good service for their owners.

POSTSCRIPT

Celestron and Losmandy have been responsive to what suggestions or criticisms have been offered by C-7 and customers about this product. Among these the tube arrangement within the packaging is to be changed. Celestron states that since the telescope tube will balance with the standard factory accessories, the counterweights or shaft length will not be changed; it will be up to the customer is to buy an extra counterweight, or buy a counterweight shaft extension. Scott is aware of the counterweight rust and is working with the painter to prevent any future occurrences. The tripod leg tolerances will be changed; they will be offering adjustable height tripod legs. The CG-11 mounting plate will be provided with 1/4"-20 safety bolts to preclude the chance of the telescope accidentally sliding off the mount to the North or South. And more changes are forthcoming, but so is a notable price decrease for 1994. Up to April 1994 we at C-7 continue to find an occasional minor quality control problem (binding R.A. setting circle, defective or damaged motor or cable), Celestron or Company Seven have remedied these prior to the delivery of any instrument to the customer. One C-11 optical tube was sent back to Celestron by Company Seven for optical refiguring; Celestron performed the work well, promptly, and with no complaints. Since that incident the optical qualities of what we have received have been acceptable.

It should also be noted that Celestron has recently changed some of the accessories for the system. As of April of 1994, they will be offering a 26mm Plossl instead of the 30mm Ultima Plossl. Celestron is making the pole finder telescope optional, and the 8x50 illuminated finder scope has been discontinued and is now being replaced by a 7x50 straight through Pole Alignment Finder scope in a fixed (not quick release) bracket. One 22 lb. counter weight is furnished instead of two 11 lb. counter weights. The adjustable height tripod also is an attractive feature.

In 1995 the CG-11 mount bearings were upgraded to allow better rigidity with the C-11 telescope, and an ability to accept up to the massive (50 lb.) Celestron C-14 SCT optical tube assembly. Indeed this marriage has produced the Celestron CG-14 telescope which offers improved rigidity and transportability over the original fork mounted C-14.

In 1996 Scott Losmandy introduced the Model DSCH Encoder Kit; a set of two encoders with precision machined hardware to attach optical encoders for use with digital setting circle computer options to either the G-11 (and GM-8) mount. These are so well done, and protect the encoders so well that we now do confidently offer these as an option for the mount. Furthermore, all of the gear sets are also precisely machined of aluminum. When joined to an optional digital setting circle or navigation aid such as the JMI NGC series of computerized displays. These permit one to easily find or identify celestial objects; the more advanced of the available models ("NGC-MAX") incorporate an RS-232 Serial Data Port allowing the telescope encoders to communicate with astronomy software run on personal computers.

Over the years, we have asked Celestron replace several OTA cases which arrived damaged however, beginning in 1996 Celestron represents the case only as a "shipping box" in an effort to avoid having an obligation to replace those cases damaged in shipping.

Company Seven has at times been critical of manufacturers putting out product that does not meet our expectations in every regard (they weren't even tested on prisoners! Marty moans). We have used harsh words and have matured enough to regret making such comments. Celestron and Losmandy, and most other successful manufacturers are good people with justifiable pride in their accomplishments. Their intent is to provide the consumer with the best value they can for the money. We can say Celestron and Scott Losmandy have been responsive to the market with a mount of this performance at a very attractive price.

And we stand by our assertion that the Celestron CG-11 remains the best value for $4,000. or less, in a tracking, one man transportable, serious deep sky instrument.

Company Seven
Astro-Optics Division